What is spontaneous fission?
In the case of spontaneous fission, which is not caused by neutron, the original actinide of mass A itself fissions. Such a fission event must be understood as a mode of radioactive decay, like a decay. In other words, in a radioactive decay, just energy in the form of g rays, electrons (b particles), helium (a partilcles), etc., or, heavy nuclides like Xenon, Krypton, Barium, etc. could be emitted. U-238 mostly decays through a emission, while Cf-254 decays mostly through fission.
